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docs(lmxproxy): add deviation #8 — SubscriptionManager COM subscription wiring

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Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Joseph Doherty
2026-03-22 04:47:23 -04:00
parent 7bed4b901a
commit 866c73dcd4
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lmxproxy/docs/deviations.md
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@@ -50,3 +50,10 @@ Decisions made during implementation that differ from or extend the original pla
**Actual**: Write is confirmed synchronously — if `_lmxProxy.Write()` returns without throwing, the write succeeded. The `OnWriteComplete` callback is kept wired for diagnostic logging only.
**Why**: MxAccess completes supervisory writes synchronously. The `OnWriteComplete` COM callback never fires for simple supervisory writes, causing the original implementation to timeout waiting for a callback that would never arrive. This caused WriteAndReadBack and WriteBatchAndWait integration tests to fail.
**How to apply**: Do not await `OnWriteComplete` for write confirmation. The `Write()` COM call succeeding (not throwing a COM exception) is the confirmation. Clean up (UnAdvise + RemoveItem) happens immediately after the write in a finally block.
## 8. SubscriptionManager must create MxAccess COM subscriptions
**Plan specified**: SubscriptionManager manages per-client channels and routes updates from MxAccess.
**Actual**: SubscriptionManager must also call `IScadaClient.SubscribeAsync()` to create the underlying COM subscriptions when a tag is first subscribed, and dispose them when the last client unsubscribes.
**Why**: The Phase 2 implementation tracked client-to-tag routing in internal dictionaries but never called `MxAccessClient.SubscribeAsync()` to create the actual MxAccess COM subscriptions (`AddItem` + `AdviseSupervisory`). Without the COM subscription, `OnDataChange` never fired and no updates were delivered to clients. This caused the `Subscribe_ReceivesUpdates` integration test to receive 0 updates over 30 seconds.
**How to apply**: `SubscriptionManager.Subscribe()` collects newly-seen tags (those without an existing `TagSubscription`) and calls `_scadaClient.SubscribeAsync()` for them, passing `OnTagValueChanged` as the callback. The returned `IAsyncDisposable` handles are tracked in `_mxAccessHandles` per address and disposed in `UnsubscribeClient()` when the last client for a tag leaves.